Quantifying insect pollinator exposure and effects from pesticides for risk and impact assessment

Pollinator populations are suffering significant declines worldwide. The use of agricultural pesticides has been identified as one of the main contributing causes. The impact pathway associated with pollinators’ exposure to pesticides, however, is currently missing in various assessment frameworks, including comparative risk screening and life cycle impact assessment (LCIA) to characterize various impacts contributing to damages on humans, ecosystems and natural resources associated with product and service life cycles.

To address this gap, we developed a model to quantify field exposure of honey bees--chosen as most relevant pollinator species--to pesticides and related potential ecotoxicity impacts. As exposure metrics, we defined bee intake and dermal contact fractions for oral and dermal exposure, respectively.

We tested our model to characterize bee impacts of two pesticides, namely lambda-cyhalothrin (insecticide) and boscalid (fungicide) applied to oilseed rape. We observed that dermal contact and oral intake fractions vary according to the specific type of forager honey bees, with the highest dermal contact fraction of 1.27x10-5 kgdermal contact/kgapplied found in pollen foragers for the fungicide boscalid, and the highest intake fractions of 3.21x10^-5 and 1.90 x10^-5 kg_oral intake/kg_applied found in nectar foragers for both boscalid and lambda-cyhalothrin respectively.

Hive oral exposure fraction is higher than forager oral exposure fractions in both pesticides. For boscalid it is 7.4 to more than 100 times higher, while for lambda cyhalothrin, it is 2.1 to 32.4 times higher than the intake fraction of foragers. We observed a higher impact of the insecticide, being the impact score two orders of magnitude higher compared with the fungicide, and the impact per unit application three orders of magnitude higher.

Overall, nectar foragers are the most affected forager type for both pesticides, emphasizing the oral pathway dominating overall bee exposure.Considering the in-hive exposure, CFs for hive bees are up to two orders of magnitude higher than CFs of foragers for boscalid, and at least twice the CF of foragers for lambda-cyhalothrin.

This is based on the assumption of the same toxicity between adults and larvae. This model and the calculation of bee intake fraction constitutes an important first step toward integrating pollinator impacts in risk screening and LCIA, whereas we also identified areas of further model refinement to fully operationalize our approach in comparative frameworks where quantifying impacts on pollinators is relevant.